Voltage at emiter Q7

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

I have a reasonably well working Soundlab. My only problem is signal bleed through from the square waves of the LFO and OSC2 into the noise generator. There's another thread about that somewhere.

However, buried in that thread is an observation that might be related (or the cause). In the docs for the Soundlab, it says:

Uncle Krunkus · Posted: Fri Nov 04, 2005 2:38 am Post subject:

The way I see it.
Based on my fairly limited circuit analysis skills.
You need to ask "what is the resistance of the reverse biased EB junction" if it's exactly 1M (R96) then you'd read 0V. If it's >1M then you'll read a positive voltage, if it's less then you'll read a negative. This is assuming you actually have + & - 9V across the junction/R96 divider (ie: - the supply, check this too)
Now if that is all okay then a reading of 1V will mean that the junction has a resistance of 1M25. Lowering R96 to about 360K would force the reading to around 5V. BUT,........ This will increase the current through the junction, which could change it's resistance. (I doubt it though)
I'm going to check out what the reading is on mine.
I'll let you know what I find out.
Andrew